The invention relates to a semicircular radial antenna having a wide-angle beam used within the range of GHz to tens of GHz.
A horn antenna has generally been known as an antenna for radiating, in the form of a beam, a radio wave within the range of GHz to tens of GHz. Since the horn antenna has a narrow angle of horizontal radiation, consideration has recently been given to a semicircular radial antenna having a wide-angle beam radiation characteristic.
The semicircular radial antenna comprises a semicircular upper waveguide plate and a semicircular lower waveguide plate. The waveguide plates are spaced a predetermined distance from each other so as to oppose each other. Base portions (i.e., linear edges) of the waveguide plates are short-circuited by a short-circuit wall, thereby constituting a semicircular radial waveguide between the upper and lower waveguide plates. Power is externally fed to the semicircular radial waveguide. Such an antenna can achieve a wide-angle beam characteristic such that half width is about 120xc2x0.
As mentioned above, the semicircular radial antenna achieves a wide-angle beam characteristic. However, there has not been considered the relationship among the structure of semicircular antenna, the horizontal beam width and the orientation of a radiated vertical beam. In addition, improvements in gains thereof are further expected.
In recent years, a radio wave in a GHz band is used in many cases in a communication system such as a satellite broadcast, a GPS, a mobile terminal, an ETC (Electronic Toll Collection) system, etc. For example, a 2.5 GHz band is used in the satellite broadcast and a 2 GHz band is used in the mobile terminal. Further, a 1.5 GHz band is used in the GPS and a 5 GHz band is used in the ETC. Further, the arriving direction of the radio wave in the satellite broadcast and the GPS is the zenithal direction. The arriving direction of the radio wave in the mobile terminal is the horizontal direction. Accordingly, these arriving directions are different from each other. Therefore, the radio wave as an object is conventionally received by using a dedicated antenna with respect to each communication system.
In this situation, it is necessary to arrange plural kinds of antennas when plural communication systems are utilized. It is complicated to arrange the plural kinds of antennas in this way, and the required area to arrange the antennas is increased. Accordingly, it is desired to receive the radio wave by a single kind of antenna in the plural communication systems. However, when the radio wave of each communication system is received by a single kind of antenna, since the arriving directions of the radio wave are different from each other as described the above, it was difficult to practically use the antenna since multidirectivity was required.
It is therefore a first object of the invention to provide a semicircular antenna which is capable of variably setting the width of a horizontal beam and change the orientation of a vertical beam radiation.
A second object of the invention is to provide a semicircular radial antenna capable of improving a gain thereof.
A third object of the present invention is to provide a multidirectional antenna in which plural radio waves having different arriving directions can be received by a semicircular radial antenna.
In order to achieve the above objects, according to the present invention, there is provided a semicircular radial antenna, comprising:
a pair of semicircular waveguide plates, having a pair of linear edge portions, an arcuate edge portion defined between the linear edge portions, the waveguide plates spaced from each other in a vertical direction;
a connecting member, which physically and electrically connects at least a part of the linear edge portions in each waveguide plate; and
a power feeder, provided between the waveguide plates while being spaced from the connecting member,
wherein at least one of the following requirements is satisfied:
i) a position of a curvature center of the arcuate portion in at least one of the waveguide plates is selected between the connecting member and the power feeder, in accordance with a desired horizontal beam radiation characteristic;
ii) a curvature radius of the arcuate portion in at least one of the waveguide plates is selected in accordance with a desired vertical beam radiation characteristic; and
iii) a slanted angle of a peripheral face of the arcuate portion, which connects a top face and a bottom face of each waveguide plate, in at least one of the waveguide plates is selected in accordance with a desired vertical beam radiation characteristic.
Here, the term xe2x80x9csemicircularxe2x80x9d does not mean xe2x80x9ccomplete half-circlexe2x80x9d, but xe2x80x9cincomplete circlexe2x80x9d. Furthermore, the xe2x80x9clinear edgexe2x80x9d may be curved if the required beam radiation characteristic is obtained.
Preferably, at least one of the waveguide plates is slidably fixed on the connecting member such that the position of the curvature center is adjustable.
Alternatively, it is preferable that at least one of the waveguide plates is detachably fixed on the connecting member.
According to the above configurations, the width of a horizontal beam and/or the orientation of a vertical radiation beam can be arbitrarily adjusted.
Preferably, the semicircular radial antenna further comprises:
a first plate member disposed on a top face of an upper waveguide plate so as to form a groove between the top face and the plate member and along the arcuate portion; and
a second plate member disposed on a bottom face of a lower waveguide plate so as to form a groove extending along the arcuate portion between the bottom face and the plate member.
Preferably, the peripheral face of the arcuate portion is formed with at least one groove extending along the arcuate portion.
Here, it is preferable that an interval between the grooves is determined in accordance with a tilt angle of a beam radiation in the vertical direction.
Further, it is preferable that the semicircular radial antenna further comprises extended portions protruded from a top face of an upper waveguide plate and a bottom face of a lower waveguide plate in the vertical direction, and extending along the arcuate portion of each waveguide plate, each extended portion being formed with at least one groove extending along the arcuate portion.
Here, it is preferable that the semicircular radial antenna further comprises a dielectric member formed along the peripheral face of the arcuate portion and a peripheral face of each extended portion.
Preferably, the semicircular radial antenna further comprises a dielectric member formed along the peripheral face of the arcuate portion. Here, a peripheral face of the dielectric member is formed with a plurality of grooves extending along the arcuate portion at positions where are substantially opposing to the peripheral faces of the arcuate portions in the respective waveguide plates.
Here, it is preferable that an interval between the grooves is determined in accordance with a tilt angle of a beam radiation in the vertical direction.
Preferably, the semicircular radial antenna further comprises a dielectric member formed along the peripheral face of the arcuate portion. Here, a peripheral face of the dielectric member is formed with a plurality of metal strip lines extending along the arcuate portion at positions where are substantially opposing to the peripheral faces of the arcuate portions in the respective waveguide plates.
Here, it is preferable that an interval between the metal strip line is determined in accordance with a tilt angle of a beam radiation in the vertical direction.
According to the above configurations, the unnecessary backward radiation can be reduced and the gains can be enhanced.
In addition, changing the interval among the plural grooves suitably, the radiation beams can be titled in the vertical direction.
Preferably, the semicircular radial antenna further comprises a combiner through which the semicircular radial antenna is connected with at least one semicircular radial antenna having the same configuration. Here, the combiner combines signals obtained from each power feeder.
Here, it is preferable that the semicircular radial antenna further comprises a switch for selecting a signal outputted from the combiner or a signal obtained from the power feeder of one semicircular radial antenna.
Further, it is preferable that the semicircular radial antenna further comprises a phase shifter which shifts a phase of a signal obtained from the power feeder so as to receive a circularly polarized wave signal together with another semicircular radial antenna.
Still further, it is preferable that the semicircular radial antenna further comprises a phase shifter which shifts a phase of a signal obtained from the power feeder so as to receive a linearly polarized wave signal together with another semicircular radial antenna.
Still further, it is preferable that the semicircular radial antenna further comprises:
a first combiner, through which the semicircular radial antenna is connected with at least one semicircular radial antenna having the same configuration;
a phase shifter which shifts a phase of a signal obtained from the power feeder so as to receive a circularly polarized wave signal together with another semicircular radial antenna; and
a second combiner, through which the semicircular radial antenna is connected with another semicircular radial antenna via the phase shifter.
Here, it is preferable that the semicircular radial antenna further comprises a branching filter which transmits a signal having a first frequency to the first combiner and a signal having a second frequency to the second combiner.
Alternatively, it is preferable that the semicircular radial antenna further comprises:
a first combiner, through which the semicircular radial antenna is connected with at least one semicircular radial antenna having the same configuration;
a phase shifter which shifts a phase of a signal obtained from the power feeder so as to receive a linearly polarized wave signal together with another semicircular radial antenna; and
a second combiner, through which the semicircular radial antenna is connected with another semicircular radial antenna via the phase shifter.
Here, it is preferable that the semicircular radial antenna further comprises a branching filter which transmits a signal having a first frequency to the first combiner and a signal having a second frequency to the second combiner.
Preferably, the semicircular radial antenna is connected with at least two semicircular radial antennas such that the semicircular radial antennas are circularly arranged at an equal interval.
Preferably, the semicircular radial antenna further comprises at least one second antenna for receiving a wave signal having a frequency higher than a frequency of a wave signal received by the semicircular radial antenna.
Preferably, the semicircular radial antenna further comprises at least two second semicircular antenna for receiving a wave signal having a frequency different from a frequency of a wave signal received by the semicircular antenna.
According to the above configurations, the multidirectivity can be attained by a single type of antenna. Furthermore, since the directivity can be switched as required, plural radio waves having different arriving directions can be received by the single type of antenna. Therefore, the antenna can be easily arranged even when an arranging area is narrow.
Preferably, the waveguide plates are provided as film substrates, and a flexible dielectric substance is placed between the waveguide plates.